Double ThumbHole Kinfe

[ASBOB]

I've gotten interested in knives that can't very easily be knocked out of your hand.

Prime example: Cold Steel has a knife with two thumb holes, one at the end of the handle, one at the juncture of handle and blade (the Double Agent). Definitely permits a secure grip.

Are there any other knives like this (preferably not karambits) that permits this kind of secure grip, and lessens the possibility of it being knocked out of your hand?

 

[Comeuppance]

Well, it's not the same kind of grip, but it's pretty difficult to knock a push knife out of a hand. It sounds like you're looking for a self-defense tool of some sort, so, these are decent options.

Also, Spyderco's Introvert would pretty much fit the bill, although it only has one ring and was admittedly made as a novelty:

 

[ScooterG]

 

[Comeuppance]

Or just combine the following two products:

...and you can call 911 and/or take some sick selfies while you're in all that deadly street combat you get into.